Magnificent Grain Refinement of Al-Mg2Si Composite by Hot Rolling

Abstract

The effect of chemical composition and the hot rolling operations on the microstructure and mechanical properties of in situ aluminum matrix composite with Mg₂Si phase as the reinforcement was studied. It was revealed that the modification by phosphorous results in the rounder (more spherical) primary and secondary (eutectic) magnesium silicide intermetallics. During hot rolling, the primary particles underwent mechanical fragmentation and the fragmented particles moved along the rolling direction. Moreover, the eutectic Mg₂Si fragmented and uniformly dispersed in the microstructure. By increasing the reduction in thickness, it was almost impossible to distinguish primary particles from eutectic ones due to excessive fragmentation of particles. These observations were related to the brittleness of Mg₂Si phase and the elongation of the matrix grains during rolling. The grain size of the matrix also changed due to the occurrence of recrystallization and the average grain size decreases from ~ 90 µm to 7 µm for the 98% rolled sample. The change in mechanical properties was related to the fragmentation of particles, destroying the eutectic network, magnificent grain refinement of the matrix, the retardation of recrystallization by the dispersed particles at grain boundaries of aluminum grains, and the fast cooling of thin sheets at high reductions in thickness.